A following method is proposed as a method for measuring an object using an image captured by a camera. Specifically, a measurer disposes or projects a marker (reference scale) having a pattern indicating a length reference in dimension on a measurement surface (a surface of a measuring object, or an extension plane of a measuring object), and captures an image of the reference scale and an object that is a measuring object by an imaging device, such as a camera, in such a manner that the reference scale and the object both fall within the image. Then, a measurement device calculates a ratio between the reference scale and the measuring object from data on the above-mentioned image, and calculates and outputs dimensions (a length, an area, a circumferential length, and the like) of the measuring object.
PTL 1 describes a method for accurately measuring dimensions by converting an image which is obliquely captured and indicates a rectangular marker with known dimensions on a measurement surface, into a front image.
PTL 2 describes a method for measuring dimensions of a rectangular parallelepiped by using a marker with known dimensions on a measurement surface.
PTL 3 describes a technique for measuring, by using a marker including a combination of a lenticular lens and a black and white pattern, a relative relationship (a position, an angle, and the like) between the marker and an observed object obtained by observing the marker, from a grayscale pattern of the marker.